The purpose of this research is to collect anatomical and physiological data which will support or refute the hypotheses that "adaptive" lung growth and accelerated lung development are initiated by increased pulmonary blook flow and/or lung stretch acting on the lungs of young animals. Morphometric techniques will be used on histological preparations of lung tissue utilizing electron microscopy to obtain adequate magnification. In addition, physiological parameters of cardiovascular and respiratory function will be measured just before the animals are sacrificed. Three experimental groups of young guinea pigs will be studied for 4 weeks and compared to control guinea pigs of similar age and body weight. The three experimental regimens are: a) animals with iatrogenic aorto-caval shunts to increase pulmonary blook flow rate without affecting metabolic rate or lung ventilation; b) unilateral phrenectomy (right) at the neck, to produce paralysis of the right hemidiaphragm and moderate collapse of the right lung and compensatory hyperventilation of the left lung, but no change in total pulmonary blook flow; and c) chronic hypercapnia to cause a sustained hyperventilation of both lungs, which produces intermittent stretch, and again with minimal impact on metabolism or lung blood flow. These studies represent an extension of ongoing research utilizing techniques that are well known to these investigators. The results of these investigations will help in the understanding of the mechanisms responsible for lung growth in a variety of clinical conditions. Currently, controversy exists concerning the factors involved in triggering the accelerated lung development in clinical as well as environmental stresses.